ASTM C1199-00(2008)
(Test Method)Standard Test Method for Measuring the Steady-State Thermal Transmittance of Fenestration Systems Using Hot Box Methods
Standard Test Method for Measuring the Steady-State Thermal Transmittance of Fenestration Systems Using Hot Box Methods
SIGNIFICANCE AND USE
This test method details the calibration and testing procedures and necessary additional temperature instrumentation required in applying Test Methods C 236, C 976, or C 1363 to measure the thermal transmittance of fenestration systems mounted vertically in the thermal chamber.
Since both temperature and surface heat transfer coefficient conditions affect results, use of recommended conditions will assist in reducing confusion caused by comparing results of tests performed under dissimilar conditions. Standardized test conditions for determining the thermal transmittance of fenestration systems are specified in Practice E 1423 and Section 5.3. However, this procedure can be used with other conditions for research purposes or product development.
It should be recognized that the only true experimental measurement is the thermal transmittance, US, value determined in Section 7. The “standardized” thermal transmittance value, UST, obtained by either the Calibration Transfer Standard (CTS) or area weighting (AW) methods described in Section 8 include adjustments to the US value that are made because the current computer calculation methods (NFRC 100-97) for determining the thermal transmittance are not capable of applying the actual surface heat transfer coefficients that exist on the test specimen while testing at standardized conditions. The current computer calculation methods assume that uniform standardized surface heat transfer coefficients exist on the indoor and outdoor fenestration product surfaces, which is not the case. Until such a time that the computer calculation methods are upgraded to have the actual surface heat transfer coefficients applied to the actual fenestration product geometry, the modification of the true tested thermal transmittance value, US, to a standardized value UST, is necessary for rating and comparison (measured with calculated) purposes.
It should be noted that the standardized surface heat transfer coefficients, hh and hs,...
SCOPE
1.1 This test method covers requirements and guidelines and specifies calibration procedures required for the measurement of the steady-state thermal transmittance of fenestration systems installed vertically in the test chamber. This test method specifies the necessary measurements to be made using measurement systems conforming to either Test Methods C 236, C 976, or C 1363 for determination of fenestration system thermal transmittance.
Note 1—This test method allows the testing of projecting fenestration products (that is, garden windows, skylights, and roof windows) installed vertically in a surround panel. Current research on skylights, roof windows, and projecting products hopefully will provide additional information that can be added to the next version of this test method so that skylight and roof windows can be tested horizontally or at some angle typical of a sloping roof.
1.2 This test method refers to the thermal transmittance, U, and the corresponding thermal resistance, R, of a fenestration system installed vertically in the absence of solar and air leakage effects.
Note 2—The methods described in this document may also be adapted for use in determining the thermal transmittance of sections of building wall, and roof and floor assemblies containing thermal anomalies, which are smaller than the hot box metering area.
1.3 This test method describes how to determine a fenestration product's (also called test specimen) thermal transmittance, US, at well-defined environmental conditions. The thermal transmittance, which is sometimes called the air-to-air U-factor, is also a reported test result from Test Methods C 236, C 976, and C 1363. If only the thermal transmittance is reported using this test method, the test report must also include a detailed description of the environmental conditions in the thermal chamber during the test as outlined in 10.3.
1.4 For rating purposes, this test method al...
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Designation:C1199–00 (Reapproved 2008)
Standard Test Method for
Measuring the Steady-State Thermal Transmittance of
Fenestration Systems Using Hot Box Methods
This standard is issued under the fixed designation C 1199; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.4 For rating purposes, this test method also describes how
to calculate a standardized thermal transmittance, U , which
1.1 This test method covers requirements and guidelines ST
can be used to compare test results from laboratories with
and specifies calibration procedures required for the measure-
different weather side wind directions and thermal chamber
ment of the steady-state thermal transmittance of fenestration
configurations, and can also be used to directly compare to
systems installed vertically in the test chamber. This test
calculated results from current computer programs for deter-
methodspecifiesthenecessarymeasurementstobemadeusing
mining the thermal transmittance of fenestration products.
measurement systems conforming to either Test Methods
Although this test method specifies two methods of calculating
C 236, C 976,or C 1363 for determination of fenestration
the standardized thermal transmittance, only the standardized
system thermal transmittance.
thermal transmittance result from one method is reported for
NOTE 1—This test method allows the testing of projecting fenestration
each test. One standardized thermal transmittance calculation
products (that is, garden windows, skylights, and roof windows) installed
procedure is the Calibration Transfer Standard (CTS) method
vertically in a surround panel. Current research on skylights, roof
and another is the area weighting (AW) method (see 4.3 and
windows, and projecting products hopefully will provide additional
Section 8 for further descriptions of these two methods). The
information that can be added to the next version of this test method so
that skylight and roof windows can be tested horizontally or at some angle area weighting method requires that the surface temperatures
typical of a sloping roof.
on both sides of the test specimen be directly measured as
specified in Practice E 1423 in order to determine the surface
1.2 This test method refers to the thermal transmittance, U,
heat transfer coefficients on the fenestration product during the
and the corresponding thermal resistance, R, of a fenestration
test. The CTS method does not use the measured surface
system installed vertically in the absence of solar and air
temperatures on the test specimen and instead utilizes the
leakage effects.
calculation of equivalent surface temperatures from calibration
NOTE 2—The methods described in this document may also be adapted
data to determine the test specimen surface heat transfer
for use in determining the thermal transmittance of sections of building
coefficients. The area weighting (AW) method shall be used
wall, and roof and floor assemblies containing thermal anomalies, which
whenever the thermal transmittance, U , is greater than 3.4
S
are smaller than the hot box metering area.
2 2
W/(m •K) {0.6 Btu/(hr•Ft •°F)}, or when the ratio of test
1.3 This test method describes how to determine a fenestra-
specimen projected surface area to wetted (that is, total heat
tion product’s (also called test specimen) thermal transmit-
transfer or developed) surface area on either side of the test
tance, U , at well-defined environmental conditions. The ther-
S
specimen is less than 0.80. Otherwise the CTS method shall be
mal transmittance, which is sometimes called the air-to-air
used to standardize the thermal transmittance results.
U-factor,isalsoareportedtestresultfromTestMethodsC 236,
1.5 Adiscussionoftheterminologyandunderlyingassump-
C 976, and C 1363. If only the thermal transmittance is
tions for measuring the thermal transmittance are included.
reported using this test method, the test report must also
1.6 The values stated in SI units are to be regarded as the
include a detailed description of the environmental conditions
standard. The values given in parentheses are provided for
in the thermal chamber during the test as outlined in 10.3.
information purposes only.
1.7 This standard does not purport to address all of the
ThistestmethodisunderthejurisdictionofASTMCommitteeC16onThermal
safety concerns, if any, associated with its use. It is the
Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal
responsibility of the user of this standard to establish appro-
Measurement.
priate safety and health practices and determine the applica-
Current edition approved Oct. 15, 2008. Published July 2009. Originally
bility of regulatory limitations prior to use.
approved in 1991. Last previous edition approved in 2000 as C 1199 – 00.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C1199–00 (2008)
2. Referenced Documents 3. Terminology
2.1 ASTM Standards: 3.1 Definitions—Definitions and terms are in accordance
C 168 Terminology Relating to Thermal Insulation withdefinitionsinTerminologiesE 631andC 168,fromwhich
C 177 Test Method for Steady-State Heat Flux Measure- the following have been selected and modified to apply to
fenestration systems. See Fig. 1 for temperature locations.
ments and Thermal Transmission Properties by Means of
the Guarded-Hot-Plate Apparatus 3.2 Definitions of Terms Specific to This Standard:
3.2.1 calibration transfer standard, n— an insulation board
C 236 Test Method for Steady-State Thermal Performance
of Building Assemblies by Means of a Guarded Hot Box that is faced with glazing, and instrumented with temperature
sensors between the glazing and the insulation board core,
C 518 Test Method for Steady-State Thermal Transmission
Properties by Means of the Heat Flow Meter Apparatus which is used to calibrate the surface resistances and the
surround panel (see Annex A1 for design guidelines for
C 976 Test Method for Thermal Performance of Building
Assemblies by Means of a Calibrated Hot Box calibration transfer standards).
3.2.2 overall thermal resistance, R , n—the temperature
C 1045 Practice for Calculating Thermal Transmission
S
Properties Under Steady-State Conditions differencebetweentheenvironmentsonthetwosidesofabody
or assembly when a unit heat flow per unit area is established
C 1114 TestMethodforSteady-StateThermalTransmission
through the body or assembly under steady-state conditions. It
Properties by Means of the Thin-Heater Apparatus
is defined as follows:
C 1363 Test Method for Thermal Performance of Building
Materials and Envelope Assemblies by Means of a Hot
R 5 1/U (1)
S S
Box Apparatus
3.2.3 standardized thermal transmittance, U , n—the heat
ST
E 283 Test Method for Determining Rate of Air Leakage
transmission in unit time through unit area of a test specimen
Through Exterior Windows, Curtain Walls, and Doors
and standardized boundary air films, induced by unit tempera-
Under Specified Pressure DifferencesAcross the Specimen
ture difference between the environments on each side. It is
E 631 Terminology of Building Constructions
calculated using the CTS method as follows:
E 783 Test Method for Field Measurement of Air Leakage
1/U 5 1/U 1~1/h –1/h !1~1/h –1/h ! (2)
ST[CTS] S STh h STc c
Through Installed Exterior Windows and Doors
E 1423 Practice for Determining Steady State Thermal and using the area weighting (AW) method:
Transmittance of Fenestration Systems
1/U 51/U 1~A /A !~1/h –1/h !1~A /A !~1/h –1/h !
ST[AW] S S h STh h S c STc c
2.2 ISO Standards:
(3)
ISO 8990 Thermal Insulation-Determination of Steady-
whereh andh arethestandardizedsurfaceheattransfer
STh STc
State Thermal Transmission Properties—Calibrated and
coefficients on the room side and weather side, respectively.
Guarded Hot Box
Their numerical values are specified in 8.2.9.1.
ISO12567–1:2000 Thermal Insulation—Determination of
3.2.3.1 Discussion—The calculation of the standardized
Thermal Resistance of Components—Hot Box Method
thermal transmittance, U , assumes that only the surface heat
ST
for Windows and Doors
transfer coefficients change from the calibrated standardized
2.3 Other Standards:
values for the conditions of the test. This assumption may not
be valid if the surface temperature differentials for the stan-
NFRC 100-97 Procedure for Determining Fenestration
Product Thermal U-factors dardized calibration conditions are different from the surface
temperaturedifferentialthatexistedforthefenestrationproduct
BS874 Part 3, Section 3.1, 1987, British Standard Methods
during the test procedure. Therefore, the standardized thermal
for Determining Thermal Insulation Properties, (Part 3,
transmittance should only be considered as an approximation
Tests for Thermal Transmittance and Conductance, Sec-
for use in comparing with calculated thermal transmittance
tion 3.1) Guarded Hot Box Method
values with standardized surface heat transfer coefficients.
BS874 Part 3, Section 3.2, 1990, British Standard Methods
for Determining Thermal Insulation Properties, Part 3,
Tests for Thermal Transmittance and Conductance, Sec-
tion 3.2 Calibrated Hot Box Method
ASHRAE Fundamentals Handbook, 1997
Withdrawn. The last approved version of this historical standard is referenced
on www.astm.org.
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org.
Available from National Fenestration Rating Council, 1300 Spring Street, Suite
120, Silver Spring, MD 20910.
Available from British Standards Institute (BSI), 389 Chiswick High Rd.,
London W4 4AL, U.K., http://www.bsi-global.com.
Available from American Society of Heating, Refrigerating, and Air-
Conditioning Engineers, Inc. (ASHRAE), 1791 Tullie Circle, NE, Atlanta, GA FIG. 1 Schematic Representation of Various Temperatures for
30329, http://www.ashrae.org. Fenestration Systems
C1199–00 (2008)
3.2.4 surface resistance, n—the temperature difference be- measured.Forinhomogeneoustestspecimens,onlythethermal
tween an isothermal surface and its surroundings when a unit transmittance, U , can be defined and measured. It is therefore
S
heat flow per unit area is established between the surface and essential to calibrate with surface heat transfer coefficients on
the surroundings under steady-state conditions by the com- the Calibration Transfer Standard (CTS) which are as close as
bined effects of convection and radiation. Subscripts h and c possible to the conventionally accepted values for building
are used to differentiate between room side and weather side design. Likewise, it would be desirable to have a surround
surface resistances, respectively. Surface resistances are calcu- panel that closely duplicates the actual wall where the fenes-
lated as follows: tration system would be installed. However, due to the wide
variety of fenestration opening designs and constructions, this
r 5 1/h (4)
h h
is not feasible. Furthermore, for high resistance fenestration
systems installed in fenestration opening designs and construc-
r 5 1/h (5)
c c
tions that are thermal bridges, the large relative amount of heat
3.2.5 surface heat transfer coeffıcient, h, n—the time rate of
transfer through the thermal bridge will cause the relatively
heat flow from a unit area of a surface to its surroundings,
small amount of heat transfer through the fenestration system
induced by a unit temperature difference between the surface
to have a larger than desirable error. As a result of the points
and the environment. (This is sometimes called surface con-
stated above, the calculation of a specimen thermal conduc-
ductance or film coeffıcient.)
tance or resistance (surface to surface) from a measured
3.2.5.1 Discussion—Subscripts are used to differentiate be-
thermal transmittance and the calculated surface heat transfer
tween room side (1 or h) and weather side (2 or c) surface
coefficients is not part of the basic measurement procedure.
conditions (see Fig. 1). It should be recognized that due to
However, by using the CTS method or the area weighting
radiation effects, the room side or weather side temperature (t
h
(AW) method described in Section 8 it is possible to obtain a
and t , respectively), may differ from the respective room side
c
standardized thermal transmittance, U , which is a rather
ST
or weather side baffle temperatures (t and t , respectively).
b1 b2
useful tool for the evaluation and comparison of experimental
If there is a difference of more than 61°C(62.0 °F), either on
results for fenestration systems with computer calculations of
the room side or weather side, the radiation effects shall be
the thermal transmittance.
accounted for to maintain accuracy in the calculated surface
3.2.6 surround panel (sometimes called the mask, mask
heat transfer coefficients. The areas used to calculate the
wall, or homogeneous wall), n—a homogeneous panel with an
surface heat transfer coefficients (Eq 6 and 8) are different
opening where the test specimen is installed (see 5.1.2 for a
depending on which method of standardization is used. When
description of a surround panel.)
the CTS Method is used to standardize the thermal transmit-
3.2.7 test specimen, n—the fenestration system or product
tance, the projected area, A , is used to calculate the surface
S
being tested.
heat transfer coefficients, whereas when using the area weight-
3.2.8 test specimen thermal transmittance, U (sometimes
ing method, the actual “wetted or heat transfer” surface area, S
called the overall coefficient of heat transfer or air-to-air
A or A , is used to determine the surface heat transfer
c
h
U-factor),n—theheattransferinunittimethroughunitareaof
coefficients.
a test specimen and its boundary air films, induced by unit
The room side and weather side surface heat transfer coefficients are
temperature difference between the environments on each side.
calculated as follows:
It is determined as follows:
when:
U 5 Q /[A •~t – t !# (10)
S S S h c
t 5 t 61°C!, (6)
~
h b1
3.3 Symbols—The symbols, terms, and units used in this
h 5 Q /[~A !~t – t !#
h S Sorh h 1
test method are as follows:
when:
t fi t ~61° C!, (7)
h b1
h 5 ~q 1 q !/~t – t ! A = total heat transfer (or developed) surface area
h r1 c1 h 1 h
when:
of test specimen on room side, m ,
A = total heat transfer (or developed) surface area
t 5 t ~61°C!, c
c b2
of test specimen on weather side, m ,
h 5 Q /[~A ! ~t – t !#
c S Sorc 2 c
A = area of room si
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:C1199–97 Designation:C1199–00 (Reapproved 2008)
Standard Test Method for
Measuring the Steady-State Thermal Transmittance of
Fenestration Systems Using Hot Box Methods
This standard is issued under the fixed designation C 1199; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers requirements and guidelines and specifies calibration procedures required for the measurement of
the steady-state thermal transmittance of fenestration systems installed vertically in the test chamber. This test method specifies
the necessary measurements to be made using measurement systems conforming to either Test Methods C 236, C 976, or C 1363
for determination of fenestration system thermal transmittance.
NOTE 1—This test method allows the testing of projecting fenestration products (that is, garden windows, skylights, and roof windows) installed
vertically in a surround panel. Current research on skylights, roof windows, and projecting products hopefully will provide additional information that
can be added to the next version of this test method so that skylight and roof windows can be tested horizontally or at some angle typical of a sloping
roof.
1.2 Thistestmethodreferstothethermaltransmittance,U,andthecorrespondingthermalresistance,R,ofafenestrationsystem
installed vertically in the absence of solar and air leakage effects.
NOTE 2—The methods described in this document may also be adapted for use in determining the thermal transmittance of sections of building wall,
and roof and floor assemblies containing thermal anomalies, which are smaller than the hot box metering area.
1.3 This test method describes how to determine a fenestration product’s (also called test specimen) thermal transmittance, U ,
S
at well-defined environmental conditions. The thermal transmittance, which is sometimes called the air-to-air U-factor, is also a
reported test result from Test Methods C 236, C 976, and C 1363. If only the thermal transmittance is reported using this test
method, the test report must also include a detailed description of the environmental conditions in the thermal chamber during the
test as outlined in 10.3.
1.4 For rating purposes, this test method also describes how to calculate a standardized thermal transmittance, U , which can
ST
be used to compare test results from laboratories with different weather side wind directions and thermal chamber configurations,
and can also be used to directly compare to calculated results from current computer programs for determining the thermal
transmittance of fenestration products. Although this test method specifies two methods of calculating the standardized thermal
transmittance, only the standardized thermal transmittance result from one method is reported for each test. One standardized
thermal transmittance calculation procedure is the Calibration Transfer Standard (CTS) method and another is the area weighting
(AW) method (see 4.3 and Section 8 for further descriptions of these two methods). The area weighting method requires that the
surface temperatures on both sides of the test specimen be directly measured as specified in Practice E 1423 in order to determine
thesurfaceheattransfercoefficientsonthefenestrationproductduringthetest.TheCTSmethoddoesnotusethemeasuredsurface
temperatures on the test specimen and instead utilizes the calculation of equivalent surface temperatures from calibration data to
determinethetestspecimensurfaceheattransfercoefficients.Theareaweighting(AW)methodshallbeusedwheneverthethermal
2 2
transmittance, U , is greater than 3.4 W/(m •K) {0.6 Btu/(hr•Ft •°F)}, or when the ratio of test specimen projected surface area
S
to wetted (that is, total heat transfer or developed) surface area on either side of the test specimen is less than 0.75.0.80. Otherwise
the CTS method shall be used to standardize the thermal transmittance results.
1.5 A discussion of the terminology and underlying assumptions for measuring the thermal transmittance are included.
1.6 ThevaluesstatedinSIunitsaretoberegardedasthestandard.Thevaluesgiveninparenthesesareprovidedforinformation
purposes only.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
This test method is under the jurisdiction of ASTM Committee C-16 C16 on Thermal Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal
Measurement.
Current edition approved Nov. 10, 1997. Published July 1998. Originally published as C1199–91. Last previous edition C1199–91.
Current edition approved Oct. 15, 2008. Published July 2009. Originally approved in 1991. Last previous edition approved in 2000 as C 1199 – 00.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C1199–00 (2008)
2. Referenced Documents
2.1 ASTM Standards:
C 168 Terminology Relating to Thermal Insulating Materials Terminology Relating to Thermal Insulation
C 177 Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the
Guarded-Hot-Plate Apparatus
C 236 Test Method for Steady-State Thermal Performance of Building Assemblies by Means of a Guarded Hot Box
C 518 Test Method for Steady-StateThermal Heat Flux Measurements andTransmission Properties by Means of the Heat Flow
Meter Apparatus
C 976 Test Method for Thermal Performance of Building Assemblies by Means of a Calibrated Hot Box
C 1045 Practice for Calculated Thermal Transmission Properties from Steady-State Heat Flux Measurements Practice for
Calculating Thermal Transmission Properties Under Steady-State Conditions
C 1114 Test Method for Steady-State Thermal Transmission Properties by Means of the Thin-Heater Apparatus
C 1363 Test Method for Thermal Performance of Building Materials and Envelope Assemblies by Means of a Hot Box
Apparatus
E 283 TestMethodforRateofAirLeakageThroughExteriorWindows,CurtainWalls,andDoorsTestMethodforDetermining
Rate of Air Leakage Through Exterior Windows, Curtain Walls, and Doors Under Specified Pressure Differences Across the
Specimen
E 631 Terminology of Building Constructions
E 783 Test Method for Field Measurement of Air Leakage Through Installed Exterior Windows and Doors
E 1423 Practice for Determining the Steady-StateSteady State Thermal Transmittance of Fenestration Systems
2.2 ISO Standards:
ISO 8990 Thermal Insulation-Determination of Steady-State Thermal Transmission Properties—Calibrated and Guarded Hot
Box
ISO/DIS 12567ThermalISO12567–1:2000 Thermal Insulation—Determination of Thermal Resistance of Components—Hot
Box Method for Windows and Doors
2.3 Other Standards:
NFRC 100-97 Procedure for Determining Fenestration Product Thermal U-factors
BS874 Part 3, Section 3.1, 1987, British Standard Methods for Determining Thermal Insulation Properties, (Part 3, Tests for
Thermal Transmittance and Conductance, Section 3.1) Guarded Hot Box Method
BS874 Part 3, Section 3.2, 1990, British Standard Methods for Determining Thermal Insulation Properties, Part 3, Tests for
Thermal Transmittance and Conductance, Section 3.2 Calibrated Hot Box Method
ASHRAE Fundamentals Handbook, 1997
3. Terminology
3.1 Definitions— Definitions and terms are in accordance with definitions in Terminologies E 631 and C 168, from which the
following have been selected and modified to apply to fenestration systems. See Fig. 1 for temperature locations.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 calibration transfer standard, n— an insulation board that is faced with glazing, and instrumented with temperature
sensors between the glazing and the insulation board core, which is used to calibrate the surface resistances and the surround panel
(see Annex A1 for design guidelines for calibration transfer standards).
3.2.2 overall thermal resistance, R , n—the temperature difference between the environments on the two sides of a body or
S
assemblywhenaunitheatflowperunitareaisestablishedthroughthebodyorassemblyundersteady-stateconditions.Itisdefined
as follows:
R 5 1/U (1)
S S
3.2.3 standardized thermal transmittance, U , n—the heat transmission in unit time through unit area of a test specimen and
ST
standardized boundary air films, induced by unit temperature difference between the environments on each side. It is calculated
using the CTS method as follows:
1/U 5 1/U 1 1/h –1/h !1 1/h –1/h ! (2)
~ ~
ST[CTS] S STh h STc c
Annual Book of ASTM Standards, Vol 04.06.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Annual Book of ASTM Standards, Vol 04.07.
Available from National Fenestration Rating Council, 1300 Spring Street, Suite 120, Silver Spring, MD 20910.
4 nd th
Available from American National Standards Institute, 11 West 42 St., 13 Floor, New York, NY 10036.
Available from British Standards Institute (BSI), 389 Chiswick High Rd., London W4 4AL, U.K., http://www.bsi-global.com.
Available from National Fenestration Rating Council, 1300 Spring Street, Suite 120, Silver Spring, MD 20910.
Available from American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (ASHRAE), 1791 Tullie Circle, NE, Atlanta, GA 30329,
http://www.ashrae.org.
C1199–00 (2008)
FIG. 1 Schematic Representation of Various Temperatures for
Fenestration Systems
and using the area weighting (AW) method:
1/U 51/U 1~A /A !~1/h –1/h !1~A /A !~1/h –1/h ! (3)
ST[AW] S S h STh h S c STc c
where h and h are the standardized surface heat transfer coefficients on the room side and weather side, respectively. Their
STh STc
numerical values are specified in 8.2.9.1.
3.2.3.1 Discussion—The calculation of the standardized thermal transmittance, U , assumes that only the surface heat transfer
ST
coefficients change from the calibrated standardized values for the conditions of the test. This assumption may not be valid if the
surface temperature differentials for the standardized calibration conditions are different from the surface temperature differential
that existed for the fenestration product during the test procedure. Therefore, the standardized thermal transmittance should only
be considered as an approximation for use in comparing with calculated thermal transmittance values with standardized surface
heat transfer coefficients.
3.2.4 surface resistance, n—the temperature difference between an isothermal surface and its surroundings when a unit heat
flow per unit area is established between the surface and the surroundings under steady-state conditions by the combined effects
of convection and radiation. Subscripts h and c are used to differentiate between room side and weather side surface resistances,
respectively. Surface resistances are calculated as follows:
r 5 1/h (4)
h h
r 5 1/h (5)
c c
3.2.5 surface heat transfer coeffıcient, h, n—the time rate of heat flow from a unit area of a surface to its surroundings, induced
by a unit temperature difference between the surface and the environment. (This is sometimes called surface conductance or film
coeffıcient.)
3.2.5.1 Discussion—Subscripts are used to differentiate between room side (1 or h) and weather side (2 or c) surface conditions
(seeFig.1).Itshouldberecognizedthatduetoradiationeffects,theroomsideorweathersidetemperature(t and t ,respectively),
h c
may differ from the respective room side or weather side baffle temperatures (t and t , respectively). If there is a difference of
b1 b2
more than 61°C(62.0 °F), either on the room side or weather side, the radiation effects mustshall be accounted for to maintain
accuracy in the calculated surface heat transfer coefficients. The areas used to calculate the surface heat transfer coefficients (Eq
6 and 8) are different depending on which method of standardization is used. When the CTS Method is used to standardize the
thermaltransmittance,theprojectedarea, A ,isusedtocalculatethesurfaceheattransfercoefficients,whereaswhenusingthearea
S
weighting method, the actual “wetted or heat transfer” surface area, A or A , is used to determine the surface heat transfer
h c
coefficients.
The room side and weather side surface heat transfer coefficients are calculated as follows:
when:
t 5 t ~61°C!, (6)
h b1
h 5 Q /[~A !~t – t !#
h S Sorh h 1
when:
t fi t ~61° C!, (7)
h b1
h 5 ~q 1 q !/~t – t !
h r1 c1 h 1
when:
t 5 t ~61°C!,
c b2
h 5 Q /[~A ! ~t – t !#
c S Sorc 2 c
when: !#
C1199–00 (2008)
when:
t fi t ~6 1°C!, (8)
c b2
h 5 q 1 q !/ t – t ! (9)
~ ~
c r2 c2 2 c
3.2.5.2 Discussion—When testing inhomogeneous test specimens, the test specimen surface temperatures and surface heat
transfer coefficients will not be exactly the same as those obtained using the calibration transfer standard. As a consequence, the
surface heat transfer coefficients obtained using the calibration transfer standard cannot be unambiguously defined and hence a test
specimen conductance cannot be defined and measured. For inhomogeneous test specimens, only the thermal transmittance, U ,
S
can be defined and measured. It is therefore essential to calibrate with surface heat transfer coefficients on the Calibration Transfer
Standard (CTS) which are as close as possible to the conventionally accepted values for building design. Likewise, it would be
desirable to have a surround panel that closely duplicates the actual wall where the fenestration system would be installed.
However, due to the wide variety of fenestration opening designs and constructions, this is not feasible. Furthermore, for high
resistance fenestration systems installed in fenestration opening designs and constructions that are thermal bridges, the large
relative amount of heat transfer through the thermal bridge will cause the relatively small amount of heat transfer through the
fenestrationsystemtohavealargerthandesirableerror.Asaresultofthepointsstatedabove,thecalculationofaspecimenthermal
conductance or resistance (surface to surface) from a
...
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